The production of highly specialized titanium alloys and especially titanium alloys utilized primarily for aircraft and spacecraft purposes, particularly the alloy Ti-5Al-2Sn-2Zr-4Mo-4Cr are known, all Aerospace Material Specifications (Society of Automotive Engineers) AMS 4975B (1968) and AMS 4975A (1968).
Subject titanium alloys are especially desirable because they can be subjected to extreme conditions in use.
However, the quality of these alloys is strictly determined by the ratios of the respective alloying elements to one another and by the purity of the product so that the fabrication of such titanium alloys has posed problems heretofore.
Titanium alloys of this composition have been produced in the past by combining titanium sponge with a two-component or binary master alloy, for example, composed of aluminum and molybdenum with metallic components such as zirconium (as zirconium sponge) and tin.
The mixture is worked up into consumable electrodes which are melted into the bath in a vacuum-electric-arc furnace in which the consumable electrode contributes the alloying elements to the titanium melt. The alloy melt is then cast into ingots.
Frequent remelting is required to ensure a sufficient homogeneity of the solid titanium alloy product thus produced (see Metall, vol. 36, pp 659 ff, 1982).
It is known to produce titanium alloys utilizing master alloys which contain, apart from aluminum, the elements zirconium, molybdenum, titanium and a variety of impurities. These known master alloys, however, do not cover the entire range of interesting and important titanium alloys with respect to the alloying elements. As a consequence, it has been necessary heretofore, especially for the production of the titanium alloys mentioned first above, to add further elements as alloying ingredients. The alloying elements in the master alloy generally cannot be found in their ratio in the master alloy or composition, in the titanium alloy which is produced.
The master alloy may be formed aluminothermically (German open application DE-OS No. 28 21 406).
I have found that these earlier methods and master alloys were incapable of producing final titanium alloys of the preferred composition in accordance with the cited Aerospace Material Specifications, for example, Ti-6Al-2Sn-4Zr-2Mo or such alloys which are closely similar thereto and can be described by the formulation Ti-5Al-2Sn-2Zr-4Mo-4Cr.
Especially noteworthy with respect to the defects of the prior art systems were the tendency toward high nitride inclusions, the tendency for incorporation of oxygen into the titanium alloys and the formation of oxide inclusions.